Which one of the following compounds is prepared in the laboratory from benzene by a substitution reaction ?

Options

A. Glyoxal
B. Cyclohexane
C. Acetophenone
D. Hexabromo cyclohexane

Answer

To determine which compound can be prepared in the laboratory from benzene by a substitution reaction, we need to analyze the options given (though they are not explicitly listed in the question). The most common substitution reaction involving benzene is the electrophilic aromatic substitution reaction.

### Step-by-Step Solution:

1. **Identify the Reaction Type**:
- We are looking for a substitution reaction involving benzene. The most common type of substitution reaction for benzene is the electrophilic aromatic substitution.

2. **Consider the Compounds**:
- The compounds that can be synthesized from benzene typically include derivatives such as alkyl groups, acyl groups, or halogens.

3. **Electrophilic Aromatic Substitution**:
- In electrophilic aromatic substitution, an electrophile replaces one of the hydrogen atoms on the benzene ring. For example, if we want to prepare acetophenone (C6H5COCH3), we can use the Friedel-Crafts acylation reaction.

4. **Friedel-Crafts Acylation**:
- To synthesize acetophenone from benzene, we can react benzene with an acyl chloride (like acetyl chloride, CH3COCl) in the presence of a Lewis acid catalyst (such as AlCl3).
- The reaction proceeds as follows:
- Benzene reacts with acetyl chloride in the presence of AlCl3.
- The AlCl3 activates the acyl chloride, generating an electrophile (the acylium ion).
- The electrophile attacks the benzene ring, substituting one hydrogen atom and forming acetophenone.

5. **Conclusion**:
- Among the possible compounds, acetophenone is prepared from benzene through an electrophilic substitution reaction (Friedel-Crafts acylation).

### Final Answer:
The compound prepared in the laboratory from benzene by a substitution reaction is **acetophenone**.